1. Field of Invention
The field of the currently claimed embodiments of this invention relates to multi-force sensing instruments, robotic systems that incorporate the instruments, and methods of use.
2. Discussion of Related Art
Retinal microsurgery refers to intraocular surgical treatment of disorders related to the retina, vitreous, and macula of the eye. Typical diseases include retina detachment, macular degeneration, and diabetic retinopathy. Retinal microsurgery demands advanced surgical skills that are near or beyond natural human capabilities. During retinal microsurgery, a surgical microscope is placed above the patient to provide magnified visualization of the interior of the eye. The surgeon inserts small instruments (e.g. 25 Ga) through trocars on the sclera, the white part of the eye, to perform delicate tissue manipulation in the posterior of the eye.
An example of a common surgical task is epiretinal membrane (ERM) peeling to restore the patient's vision from ERM distortion. The surgeon carefully peels the thin, semi-transparent scar tissue (the ERM) off the retina using a micro-forceps, as shown in FIGS. 1A and 1B. Steady and precise motion is desired, because the thickness of the ERM 1 can be an order of magnitude smaller than human hand tremor 2. Additionally the force applied on the ERM has to stay below the strength of the retina tissue. However, the forces exerted between the instrument tip and the retina are well below the human sensory threshold 1. The absence of force sensing raises the risk of applying excessive force on the retina, which can potentially cause retina hemorrhage and tearing. During the ERM peeling, the eye should be stable to minimize the motion of the target membrane. This requires the tool motion to comply at the sclerotomy site. Only three rotational degrees of freedom (DOF) about the sclera entry point and one translational DOF along the instrument axis are allowed, while lateral translations are prohibited by the sclera constraint. This corresponds to the concept of remote center-of-motion (RCM) in robotics, devised by Taylor et al. 4. A fixed RCM is often considered to be a fundamental requirement in minimally invasive Surgery (MIS).
Unlike MIS, the imaging component of retinal microsurgery, the microscope, is located outside the patient and is rarely moved, as shown in FIG. 1A. Instead, the retinal surgeon needs to reposition the patient's eye while the tools are inserted, in order to adjust the view and gain tool access to the region of interest. As a result, the location of the RCM point (the sclera entry point) is not necessarily fixed, and can move up to 12 mm during retinal microsurgery 5. The repositioning of the eye requires all of the instruments inserted in the eye (e.g. a micro-forceps and a light pipe) to move in coordination. Unsynchronized instrument motion can cause cornea striae, which distorts the view of the retina in the microscope. Suboptimal ergonomics and fatigue impose further limitations on surgical performance.
Many robotic systems have been developed and investigated to explore the potential to enhance and expand the capabilities of retinal surgery and microsurgery in general. Master-slave teleoperated robotic systems 6-10 have the advantage of motion scaling to achieve high precision. Building both master and slave robots results in complex systems and high cost. Furthermore, the surgeon's perception of the interaction between the slave robot and the patient is inadequate. Another approach is handheld robotic devices that provide active tremor cancellation 1112. Despite increased size and weight attributed to additional actuators, these devices provide an intuitive interface. However, the workspace is constrained by the tracking system and scaled feedback of the human-imperceptible forces cannot be implemented. The third approach is untethered micro-robots moved by controlled nonuniform magnetic fields 13. The untethered control enables a large workspace and complex maneuvers. The drawbacks include the large footprint and limited surgical application.
Some embodiments of the current invention can use the Steady-Hand Eye Robot with hands-on cooperative control 14-17, where the user and the robot both hold the surgical instrument. The user input force applied on the instrument handle controls the velocity with which the robot follows the user motion. This control approach is also termed admittance velocity control. The human hand tremor is damped by the stiff robot structure. The cooperatively controlled robot provides not only the precision and sensitivity of a machine, but also the manipulative transparency and immediacy of hand-held instruments. This robotic system can further be augmented with virtual fixtures 18, as well as incorporated with smart instruments with various sensing modalities.
Virtual fixtures are algorithms that provide assistive motion guidance with anisotropic robot behavior. The robot motion constraints assist the user to avoid forbidden regions 1819, as well as to guide along desired paths 2021. Virtual fixtures can be prescribed 1819, generated from patient anatomy 22 or from real-time computer vision 20. The implementation includes impedance 19 and admittance methods 2021, as well as optimization algorithms with desired geometric constraints 2223. With the aid of virtual fixtures, the mental and physical demands on the user to accomplish a desired maneuver are reduced, while the task performance is notably increased. The surgeon can concentrate on the critical surgical tasks (e.g. ERM peeling) if virtual fixtures can manage the inherent surgical motion constraints, such as RCM and tool coordination, by providing an intuitive, guided robot behavior.
Smart instruments with force sensing capability are essential for safe interaction between the robot and the patient. Various force sensors have been developed for microsurgery, micromanipulation, and MIS 24-28. Handle mounted force sensors 29 cannot distinguish forces exerted at the tool tip from those at the trocar. Therefore, a family of force sensing instruments 30-33 has been developed with fiber optic sensors integrated into the distal portion of the instrument that is typically located inside the eye. Auditory 34 and haptic 35 force feedbacks have demonstrated the efficacy of regulating the tool-to-tissue interaction force. During a freehand manipulation, the surgeon can often sense the contact force at the sclera entry point, and utilizes it as an important indicator to guide the desired motion, e.g. RCM and tool coordination. However, the stiffness of the Steady-Hand Eye Robot attenuates the user perceptible level of the sclera force, inducing undesired large sclera forces. We devised a dual force sensing instrument 36 to provide force feedback from both tool tip force and sclera force. The drawback is that the force sensor cannot provide the sclera force value and the location where the sclera force is applied on the tool shaft. Instead, it measures the moment attributed to the sclera force. Therefore, there remains a need for multi-force sensing instruments, robotic systems that incorporate the instruments, and methods of use.